<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <title>08_元素水平垂直居中</title>
    <style>
        .outer {
            width: 400px;
            height: 400px;
            background-color: #888;
            display: flex;

            /* 方案一 */
            /* justify-content: center; */
            /* align-items: center; */
        }
        .inner {
            width: 100px;
            height: 100px;
            background-color: orange;
            /* 方案二 */
            margin: auto;
        }
    </style>
</head>
<body>
    <div class="outer">
        <div class="inner"></div>
    </div>
</body>
</html>